This was a long holiday weekend in Bangkok. In case you are wondering, May 17 (this year) is Visakha Bucha Day. It’s a Buddhist holiday and is often called Buddha’s birthday, though that isn’t really an accurate name. It might be better to refer to it as Buddha’s life day, as it is a celebration of the founder of Buddhism, Siddhartha Gautama’s birth, enlightenment (when he reached nirvana), and death. The day of celebration is determined by a lunar calendar and is officially the full moon of May. Governments may bridge gap days to tie it to a weekend.
For Buddhists this is a day to get to the temple and walk three times around the ubosot in meditation while the head monk gives a sermon and leads the chanting. One should also respect the precepts of Buddhism today (which any Buddhist ought to already be doing anyway, right?) and in many cases, eat vegetarian. (Don’t kill anything, not even a mosquito. Wear white, use repellent, and hope for the best, people.)
Be aware that alcohol sales are prohibited, though there are always those few (many?) random places serving foreigners that somehow pull it off.